Generally, a refrigeration equipment with a wide range of temperature control is used primarily with the containers that are subject, in operation, to a wide range of temperature fluctuations of ambient air. Namely, the refrigeration equipment for container use so far known is so constructed as to usually perform two modes of operations, that is, refrigeration operation to control the hold temperature of container at a low temperature below -5.degree. C. or -6.degree. C. of refrigeration domain and cold storage operation to control said temperature at a high temperature above -5.degree. C. or -6.degree. C. of chilled domain. To this end, the capacity of the container refrigeration equipment is set at the capacity requirement of refrigeration operation, that is, at the capacity sufficient to keep the hold temperature, for example, at -18.degree. C. under the ambient air temperature of 38.degree. C.
Therefore, in case of cold storage operation to maintain the hold temperature within chilled domain, there arises an excess capacity under the condition of low ambient air temperature, resulting in a problem of being unable to maintain the desired hold temperature.
In order to solve said problem, it has been suggested to control the hold temperature by installing a hot gas by-pass passage, bridging between high pressure gas line and low pressure liquid line and introducing hot gas to the evaporator therethrough.
While the refrigeration equipment of the conventional method is also shown in the description and drawings of U.S. Pat. No. 3,692,100, it is so constructed, as shown in FIG. 10, as to install, on the high pressure gas line connecting the discharge side of a compressor A with the inlet side of an air-cooled condensor C.sub.1, a hot gas by-pass passage by-passing said condenser C.sub.1, water-cooled condenser C.sub.2, drier R and expansion valve EV, all in-series connected, a solenoid valve SV and a temperature control valve TV with a sensor T, on said hot gas by-pass passage, thus it is able to control the hold temperature within chilled domain through the temperature control of supply air under hot gas by-pass operation.
Namely, in case of cold storage operation, said solenoid valve SV is open and said temperature control valve TV opened when supply air temperature is below the temperature setting, thus hot gas being fed into said low pressure liquid line D and after being mixed with liquid rerigerant fed through expansion valve EV, introduced into evaporator E. Thus it is arranged so as to control the hold temperature within chilled domain by adjusting the supply air temperature.
When the hold temperature setting is low or, even though said temperature setting is high, when ambient air temperature is higher than said temperature setting, that is, in the hatched area M of FIG. 9, it is possible with the refrigeration equipment of the conventional method to control the hold air temperature by hot gas by-pass method. However, when the temperature setting is high and the ambient air temperature is lower, that is, in the unhatched area N of FIG. 9, there arises a problem of being unable to control the hold air temperature by means of hot gas by-pass because in said area N, the heating effect decreases with the increase of refrigeration capacity.
Furthermore, said expansion valve EV is generally of the type of the thermostatic expansion valve wherein the opening is controlled by sensing the temperature of low pressure gas and as stated above, in case of the hold temperature control by means of hot gas by-pass, low pressure gas at the out-let of evaporator E becomes superheated by hot gas by-passed, the opening of said expansion valve EV with a feeler bulb attached to low pressure gas line G being increased further. As a result, even when ambient air temperature becomes lower, the liquid refrigerant flow through said expansion valve EV is increased because of the valve opening that is equal to or larger than that of the case of high ambient air temperature.
Therefore, under said condition, even if means of hot gas by-pass is employed, it is impossible to control the hold temperature because heating effect thereof is overcome by cooling effect of liquid refrigerant. Further, with the increase of valve opening of said expansion valve EV, the power in-put of compressor will also increase, thus resulting in the waste of energy and failure to meet the requirement of energy saving.